Re: [DML] Fuel sending unit / digital dash

["Walter" <Whalt@xxxx>]

Marty,

As far as the car electronics are concerned, the oil pressure gauge
functions pretty much as an ohm meter when the oil pressure sending unit is
replaced with a resistor box. The zero and 80 psi readings are accurate,
but the markings in between are logarithmically spaced to account for the
lever arm in the sending unit moving in a circular motion across a linear
rheostat track. Thus, as a percentage of full scale, the gauge is accurate
to scale proportion. i.e. 50% scale is 40 ohms. However, the 40 psi
demarcation is closer to 50 ohms. I'll have exact values ready when I get
the film in my camera developed. I did multiple exposures with multiple
gauge positions. It will look real cool when it's all done.

Look at the chart below and tell me which value I got incorrect. It seems
to me that your sending unit has the principle and idea right, but the
values it yields are incorrect. ;-)

To help explain the data, here is a quote from my yet to be published
report:

The data show that all sending units are 'sticky' meaning that there is a
bit of friction that must be over come before the inner workings of the unit
will register a change in input pressure. It took up to a 13 psi change to
cause any measurable change in sender output. Some of this static friction
may be attributed to the following:
1) senders being new and not yet broken in .
2) senders being tested at room temperature.
3) (and most important) sender not being exposed to the vibration of a
normal running engine.

I'm considering setting up a vibrating manifold for the sending units so
that I can better approximate actual working conditions for when I re-test
them. (Ah, the curse of being a Libra.)

Here's the data I found for the sending unit YOU sent me:

First number is PSI, second number is ohms yielded from sending unit on
decreasing pressures, third number is ohms yielded from sending unit on
increasing pressures. These are average values.

PSI vs. Ohms
------------------------
80.0 87.0 & 80.5

75.0 80.9 & 80.5

70.0 80.8 & 72.4

65.0 72.7 & 72.4

60.0 72.7 & 68.7

55.0 69.0 & 65.0

50.0 65.4 & 61.3

45.0 61.7 & 55.3

40.0 55.6 & 49.3

35.0 49.6 & 44.4

30.0 44.6 & 39.4

25.0 39.6 & 35.0

20.0 35.2 & 30.9

15.0 31.2 & 24.5

10.0 27.6 & 00.4

5.0 00.6 & 00.5

0.0 00.6 & 00.5

-----Original Message-----
From: wingd2@xxxx <wingd2@xxxx>
To: dmcnews@xxxxxxxxxxx <dmcnews@xxxxxxxxxxx>
Date: Friday, September 22, 2000 11:57 PM
Subject: Re: [DML] Fuel sending unit / digital dash


>Walt,
> On the fuel sending unit, you should take one apart sometime. It works
on
>the rheostat principal, just a little different design then other sending
>units.
>
> And on the oil sending unit. You've got the principle and idea of how it
>works right, it's just the values you've got are incorrect.
>
> Marty